Rabbits will be used to add blood flow and direct blood pressure observations to work in progress with mice. Whem mice are socially stressed in a complex population cage for 9 months, they develop fixed high blood pressure, arteriosclerosis, and chronic interstitial nephritis. A cardioselectice beta blocker will control blood pressure, but does not affect nephritis; and X-rays of stressed mice show development of urinary retention with reflux. It is hypothesized that the combination of this behaviorally induced urinary stasis with episodes of renal vasoconstriction, also of emotional origin, may induce tissue damage leading to chronic interstitial nephritis. We are currently studying the effects of a low salt diet as well as the beta blocker Metoprolol on renal response of mice to psychosocial stress. Parallel work on rabbits is suggested because their social behavior is similiar and they are large enough for recording renal blood flow and systemic arterial pressure chronically when-free-running. They are also more suited for chemical and stereotaxic studies of the brain. A phase delay, crystal, ultrasonic flow probe devised by us in 1971 for dogs has now been successfully miniaturized. Initial work will use hard line measures of renal blood flow with direct catheter measures of blood pressure and pulse rate to monitor responses to confrontations between pairs of rabbits in small pens. A transmitter mounted on a rabbit's head will eventually record renal blood flow data during social interaction in complex population cages housing male-female colonies. Direct catheter blood pressure will be transmitted for as long as feasible; thereafter, we will resort to sphygmomanometry, as in mice. Locomotor behavior will be followed in individuals identified by recording their frequency of transmission. Plasma renin, corticosterone, and blood urea samples will be taken monthly, and tyrosine hydroxylase and cardiorenal damage will be assessed at autopsy, as in mice. The effects of a low salt diet and of a beta blocker will be major objective of these psychosocial studies.